Fluorescent lamps of improved color rendition

ABSTRACT

A fluorescent lamp is provided on the inner wall surface of a sealed envelope with a first fluorescent layer including at least one fluorescent material selected from a group consisting of manganese activated magnesium fluorogermanate and manganese activated magnesium arsenate. On the first fluorescent layer is deposited a second fluorescent layer comprising a mixture of at least one fluorescent material selected from a group consisting of magnesium tungstate, calcium tungstate and antimony activated calcium halophosphate and at least one fluorescent material selected from a group consisting of tin activated strontiummagnesium-barium orthophosphate, tin activated calcium-strontium orthophosphate and calcium halophosphate activated with antimony and manganese. The thicknesses of the first layer and the second layer are respectively 21 + OR - 5 microns and 9 + OR - 5 microns.

United States Patent [72] Inventors [2 l Appl. No. [22] Filed [45] Patented [73] Assignee [32] Priority Teizo Hanada Saitama-ken;

Tomohiko Kobuya, Yokohama-shi, Japan 795,150

Jan. 30, 1969 Mar. 9, 1971 Tokyo Shibaura Electric Co., Ltd., Kawasaki-shi, Japan Feb. 3, 1968 Japan [54] FLUORESCENT LAMPS OF IMPROVED COLOUR OTHER REFERENCES FLUORESCENT LAMPS AND LIGHTING, by Elenbaas et al., Chapter II, Section 2.3, pages 18- 23 and Chapter III, sections3.9 3.12, pages 58- 64; 1962; copy of book in A.U. 251.

Primary Examiner.lohn Kominski Assistant ExaminerPalmer C. Demeo Attorney-Flynn and Frishauf ABSTRACT: A fluorescent lamp is provided on the inner wall surface of a sealed envelope with a first fluorescent layer including at least one fluorescent material selected from a group consisting of manganese activated magnesium fluorogermanate and manganese activated magnesium arsenate. On the first fluorescent layer is deposited a second fluorescent layer comprising a mixture of at least one fluorescent material selected from a group consisting of magnesium tungstate, calcium tungstate and antimony activated calcium halophosphate and at least one fluorescent material selected from a group consisting of tin activated strontium-magnesiumbarium orthophosphate, tin activated calcium-strontium orthophosphate and calcium halophosphate activated with antimony and manganese. The thicknesses of the first layer and the second layer are respectively 21 i 5 microns and 9 i 5 microns.

PATENTED MAR 9197:

SHEET 1 OF 2 FIG.

T5120 #1 AND & finpmro K B J,

INVENTORS FLUORESCENT LAMPS OF IMPROVED COLOUR RENDITION This invention relates to fluorescent lamps, more particularly to fluorescent lamps of improved color rendition.

In the prior art fluorescent lamps of the improved color rendition type, four or five types offluorescent materials were mixed together and the powder obtained by pulverizing the mixture is coated on the inner surface of glass tubes in order to obtain substantially uniform spectral distribution over the entire visible range.

However, the luminous energy distribution of such prior fluorescent lamps has not been improved at least with regard to mercury resonance line spectra. Especially, the outputs of mercury resonance line spectra having wavelengths of 436 nm and 546 nm manifesting large luminous energy values are not different from the outputs of conventional fluorescent lamps of white color or daylight color type. As a result, even in fluorescent lamps having characteristics close to those of an ideal light source in the continuous spectral portion, there is a problem of the color rendition that the yellow or yellowish red color emanated therefrom shifts to the side of yellowish green. Accordingly, even in the prior fluorescent lamps of improved color rendition type their CIE general color rendering index is at most about 93.

An object of this invention is to provide fluorescent lamps having greatly improved color renditions and high lamp efficiencies.

According to this invention a first fluorescent layer having a thickness of 21 :Smicrons is formed by applying on the inner wall surface of a light transmissive glass tube at least one fluorescent material selected from a group consisting of manganese-activated magnesium fluorogermanate and manganese-activated magnesium arsenate. On this first layer is formed a second layer of fluorescent material having a thickness of 9 i microns by depositing a mixture comprising at least one fluorescent material acting as a blue composition and selected from a group consisting of calcium tungstate, antimony activated calcium halophosphate and magnesium tungstate, and a fluorescent material acting as an orange composition and selected from a group consisting of tin activated calcium-strontium orthophosphate, tin activated strontiummagnesium-barium orthophosphate and calcium halophosphate activated with antimony and manganese.

The first fluorescent layer absorbs blue color to emit deep red color. This conversion from blue to deep red is effected without any appreciable energy loss, thus giving a high lamp efficiency. The second fluorescent layer manifests substantially uniform luminescence from blue to red.

According to this invention, there is provided a fluorescent lamp comprising a light transmissible-sealed envelope; coil electrodes sealed to both ends of said envelope; a quantity of mercury and an ionizable inert gas sealed in said envelope; a first fluorescent layer including at least one fluorescent material selected from a group consisting of manganese-activated magnesium fluorogermanate and manganese-activated magnesium arsenate, said first layer being deposited on the inner wall surface of said envelope and having a thickness of 21 1- 5 microns; and a second fluorescent layer deposited on said first fluorescent layer, said second fluorescent layer including a mixture of at least one fluorescent material which emanates the blue region of visible 'light rays and being selected from a group consisting of magnesium tungstate, calcium tungstate and antimony activated calcium halophosphate, and at least one fluorescent material which emanates the orange region of visible light rays and being selected from a group consisting of tin activated strontiummagnesium-barium orthophosphate, tin activated calciumstrontium orthophosphate and calcium halophosphate activated with antimony and manganese, said second fluorescent layer having a thickness of 9, i 5 microns.

The invention can be more fully understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIG. 1 shows a side view, partly in section and partly broken away, of fluorescent lamp of improved color rendition; and

FIG. 2 is a graph illustrating the luminous spectral distribution of the fluorescent lamp shown in H6. 1.

According to one embodiment of this invention a glass envelope l. was prepared having an outer diameter of 32 mm. and a length of approximately 1200 mm. and on the inner wall of the envelope was formed a first fluorescent layer 2 of 21 microns thick by depositing by means of a well known method a composition comprising a mixture of 50 percent, by weight, of manganese-activated magnesium fluorogermanate and 50 percent, by weight, of manganese-activated magnesium arsenate. On the first fluorescent layer was formed a second fluorescent layer 3 having a thickness of 9 microns by applying a composition comprising a mixture of 44 percent, by weight, of magnesium tungstate, 56 percent, by weight, of tin activated strontium-magnesium barium orthophosphate. A coil electrode 4 is sealed to each end of the glass envelope 1 with fluorescent layers applied as above-described. Attached to both ends of said envelope 1 are bases 5, 5 including a pair of pins 6, 6 respectively connected to the both ends of said coil electrode. After evacuating the envelope a quantity ofmercury and an ionizable inert gas were sealed in the envelope 1. In this manner, a fluorescent lamp having a rated'wattage of 40 W and improved color rendition was provided.

The fluorescent lamp had a color temperature of 5000" K, CIE general color rendition index Ra 98, a total light flux of 2300 lumens.

The conventional fluorescent lamp of improved color rendition but having only one deposited fluorescent layer has a general color rendition index Ra 93 and a total light flux of 2100 lumens at substantially the same color temperature. This means that the above-described embodiment has a greatly improved color rendition as well as a higher lamp efficiency when compared with such conventional fluorescent lamp.

The luminous characteristics of the fluorescent lamp of im proved color rendition will now be described by referring to FIG. 2, wherein the abscissa represents the wavelength in nm, and the ordinate the relative energy in percent and the percentage of light energy absorption of the first fluorescent layer Curve a represents the light energy absorption characteristic of the first fluorescent layer 2 whereas curve b the luminous characteristic thereof. As can be clearly noted from curves a and b the first fluorescent layer 2 well absorbs the light energies of the mercury resonant line spectra of the wavelengths of 406 nm and 436 nm, of continuous spectrum portion of deep blue region of the wavelength of less than 450 nm and of the ultraviolet region and converts these energies into deep red color essentially having a wavelength of 655 nm which is the characteristic luminous spectrum of the first fluorescent layer 2.

Curve 0 represents luminous characteristic of a fluorescent lamp having a single fluorescent layer consisting of only the fluorescent materials of said second fluorescent layer 3. The second fluorescent 'layer 3 absorbs ultraviolet rays of the wavelength of 254 nm generated by a mercury vapor discharge and converts most of the absorbed energy into visible light rays, thus emanating radiations as shown by curve 0 to manifest bluish white as a whole. By the combination of the first and second fluorescent layers, deep blue region of the wavelength of less than 450 nm of the luminous energy from second fluorescent layer 3 is absorbed by the first fluorescent layer 2 and the energy thus absorbed is converted into deep red color essentially of the wavelength of 655 nm by the action of the first fluorescent layer 2. Conversion of the deep blue region into the deep red region is accomplished without any appreciable loss of energy, which not only contributes to the improvement of the lamp efficiency but also allows to intensify the blue luminescence of the second layer as far as possible thus decreasing the percentage of the mercury resonance line spectrum of the wavelengths of 406 and 436 nm with respect to the continuous spectrum luminous energy of the blue color.

Curve has a valley" between wavelengths of 500 nm and 600 nm which well balances with the energy of mercury resonance line spectra of the wavelengths of 456 nm and 576 nm thus ensuring a uniform spectral energy distribution over the entire visible region. Further, the second fluorescent layer 3 absorbs ultraviolet rays of the wavelength of 254 nm generated by the mercury vapor discharge and converts most of the absorbed energy into visible light rays thus improving the efficiency of the fluorescent lamp.

Curve d including outputs corresponding to the resonance spectral lines of mercury represents the luminous characteristic of the illustrated fluorescent lamp embodying this invention. As curve d clearly shows, the spectral energy distribution of the fluorescent lamp is substantially uniform over the entire visible region. It will be noted that the energy of the mercury resonance line spectrum of the wavelength of 436 nm which as been considered impossible to suppress has decreased to less than two-thirds of the value of the conventional fluorescent lamps.

Although in the above embodiment the first fluorescent layer 2 was formed by a mixture of fluorescent materials comprising manganese-activated magnesium fluorogermanate and manganese-activated magnesium arsenate it should be understood that the fluorescent layer 2 may be composed of only one of these materials. Where a mixture of the materials is employed their ratio is not material to the desired result of this invention. The thickness of the first fluorescent layer 2 may be in a range of 21 i 5 microns. If the thickness of this layer were less than 16 microns the mercury resonance line spectrum of the wavelength of 436 nm would be transmitted so that the desired color rendition would not be realized. On the other hand, if the thickness of the fluorescent layer 2 were larger than 26 microns, the percentage of transmission of the emanated color light would be reduced thus decreasing the total light flux of the lamp.

In the above-described embodiment, the second fluorescent layer 3 was formed by a mixture of fluorescent materials comprising magnesium tungstate, and tin activated strontium-magnesium-barium orthophosphate, the former acting as the blue composition while the latter as the orange composition. However, it should be understood that the second fluorescent layer 3 is not limited to the specified composition. Thus, for example, as the blue composition may be used calcium tungstate or antimony activated calcium halophosphate. Alternatively, mixture of any two or three of above-described fluorescent materials (magnesium tungstate, calcium tungstate and antimony activated halophosphate) may be used at any desired ratio. As the orange composition may be used either tin activated calcium-strontium strontium orthophosphate or calcium halophosphate activated with antimony and manganese. Alternatively, mixtures of any two or three of above-described fluorescent materials (tin activated strontium-magnesiumbarium orthophosphate, tin activated calcium-strontium orthophosphate and calcium halophosphate activated with antimony and mangases) may be used at any desired ratio.

Generally, following equations hold true between the ratio of mixing the blue and orange compositions of the second fluorescent layer 3 and the color temperature of fluorescent lamps utilizing the same.

where xrepresents the weight percent of the blue composition, y the weight percent of the orange composition and Tthe color temperature in K. Generally, 3000; t7000. In the above embodiment x 44, y 56 and T 5000. It is often While in the above embodiment, the thickness of the second fluorescent layer 3 was 9 microns, this thickness may be varied within a range of 9 i 5 microns. If the thickness were less than 4 microns sufficient radiations from second layer could not be obtained, thus decreasing the color rendition. On the other hand if the thickness were larger than 14 microns the exciting energy for the first fluorescent layer would be decreased by the absorption of 254 nm by the second layer 3, thus decreasing the color rendition.

With regard to the thickness of the first and the second fluorescent layers 2 and 3 it is important that the thickness of the first fluorescent layer 2 should be 21 i 5 microns and that of the second fluorescent layer 3 should be 9 i 5 microns. Should the thickness be deviated from the specified ranges the CIE general color rendition index Ra of the resulted lamp will be outside of a range of from to 98. Some degree of nonuniformity of the thickness of the first and second fluorescent layers as measured along the length of the glass envelope of the fluorescent lamp may be permissible so long as the extent of nonuniformity in the thickness is maintained within the specified ranges. Otherwise, nonuniform luminescence would be resulted along the length of the glass envelope.

Manganese-activated magnesium fluorogermanate which is the fluorescent material constituting the first fluorescent layer of this invention is not degraded by the ultraviolet rays at elevated temperatures. Consequently, by increasing the composition of said fluorescent material, this invention can be readily applied with good results to fluorescent lamps of high output and extra high output.

We claim:

1. A fluorescent lamp comprising a light transmissible sealed envelope; coil electrodes sealed to both ends of said envelope; a quantity of mercury and an ionizable inert gas sealed in said envelope; a first fluorescent layer including at least one fluorescent material selected from a group consisting of manganese-activated magnesium fluorogermanate and manganese-activated magnesium arsenate, said first layer being deposited on the inner wall surface of said envelope and having a thickness of 21 i 5 microns; and a second fluorescent layer deposited on said first fluorescent layer, said second fluorescent layer including a mixture of at least one fluorescent material which radiates the blue region of visible radiations and being selected from a group consisting of magnesium tungstate, calcium tungstate and antimony activated calcium halophosphate, and at least one fluorescent material which radiates the orange region of visible radiations and being selected from a group consisting of tin activated strontium-magnesium-barium orthophosphate, tin activated calcium-strontium orthophosphate and calcium halophosphate activated with antimony and manganese, said second fluorescent layer having a thickness of 9 i 5 microns.

2. A fluorescent lamp according to claim 1 wherein said at least one fluorescent material functioning to radiate the blue region and said at least one fluorescent material functioning to radiate the orange region are mixed together so as to satisfy the following equations:

where x i 10 is the weight percentage of the former fluorescent material, while y l 10 is the weight percentage of the latter fluorescent material, respectively, based on the entire second fluorescent layer, and T represents the color temperature in "K of said fluorescent lamp and ranges between 3000 and 7000.

3. A fluorescent lamp according to claim 2 wherein said first fluorescent layer comprises 50 percent by weight of manganese-activated magnesium fluorogermanate and 50 percent by weight of manganese-activated magnesium fluorogermanate both percentages being based on said first fluorescent layer.

4. A fluorescent lamp according to claim 2 wherein said second fluorescent layer comprises 44 percent by weight of magnesium tungstate and 56 percent by weight of tin activated strontium-magnesium-barium orthophosphate. 

2. A fluorescent lamp according to claim 1 wherein said at least one fluorescent material functioning to radiate the blue region and said at least one fluorescent material functioning to radiate the orange region are mixed together so as to satisfy the following equations: where x + or - 10 is the weight percentage of the former fluorescent material, while y - or + 10 is the weight percentage of the latter fluorescent material, respectively, based on the entire second fluorescent layer, and T represents the color temperature in *K of said fluorescent lamp and ranges between 3000 and
 7000. 3. A fluorescent lamp according to claim 2 wherein said first fluorescent layer comprises 50 percent by weight of manganese-activated magnesium fluorogermanate and 50 percent by weight of manganese-activated magnesium fluorogermanate both percentages being based on said first fluorescent layer.
 4. A fluorescent lamp according to claim 2 wherein said second fluorescent layer comprises 44 percent by weight of magnesium tungstate and 56 percent by weight of tin activated strontium-magnesium-barium orthophosphate. 